There is an error about the age of the Moon

Since when has the Moon been orbiting the Earth? Until now, the age of our satellite was uncertain. Some researchers estimated it to be around 4.35 billion years old, others more than 4.5 billion years old.

To answer this question, an international research team composed of scientists from the University of California at Santa Cruz, the Max Plank Institute for Solar System Research (MPS) and the CNRS in France published this December 18 , in the magazine Naturea study to answer the enigma posed by the real age of the Moon.

The history of the Moon

According to scientists, the Moon formed after a giant impact on Earth that sent a boiling mass into space. This was covered by an ocean of liquid rock, called the lunar magma ocean, which crystallized over time. At that time, the Moon and Earth were not as far apart. As the first author of this study, Francis Nimmo of the University of California at Santa Cruz, explains in a press release: “We are particularly interested in the phase when the distance between the Earth and the Moon was about a third of the current distance.”

It was over time that the shape of the Moon changed and its orbit became more elliptical. This caused a change in the speed of the Moon and its distance from Earth. These variations caused a heating, from the interior of the Moon, so significant that it melted a large part of the lunar crust.

A reset of the Moon’s geological clock

The age of the Earth or the Moon can be read in the compositions of the rocks. How ? The composition of a rock will change with its environment. In a very hot environment, the rock will change its composition. On the contrary, in a cold environment, its composition will freeze. At that moment, part of its radioactive atoms, “trapped” by the cold, will gradually disintegrate and “the geological clock” se with en route.

On the surface of the Moon, researchers found a few grains of a rock called zircon. This is resistant to heat and probably remained cold in certain places in the lunar crust. The researchers proved that the zircon found was older than the rest of the rocks unearthed on the surface of the Moon. It is therefore proof that the Moon is older than previously estimated.

Thorsten Kleine, director of the MPS and co-author of the study, says: “The intense volcanism likely reset the Moon’s geological clock. The lunar rock samples therefore do not reveal their original age, but only the date when they were last strongly heated.”

The researchers conclude, in this study, that the Moon itself is between 4.43 and 4.51 billion years old (since its zircon is that much old). Its crust, meanwhile, was later reshaped by significant warming and dates to 4.35 billion years ago, which matches the previous estimate based only on rocks.

This hypothesis would explain many other puzzles posed by the Moon so far. For example, its reduced number of craters compared to its age, as Alessandro Morbidelli, co-author of the study and researcher at the CNRS, explains: “Lava from the interior of the Moon could have filled the first impact basins and thus made them unrecognizable”.